Optical neuroinformatics

ABSTRACT

A method is provided for improving cognitive performance assessment in a smooth pursuit cognitive performance test by using measurement metrics including a lead/lag metric, a radial inbounding metric, a path dependent velocity metric, a path drift metric, a velocity variability metric, or a variance statistics metric.

FIELD OF THE INVENTION

This invention relates to neuropsychological testing for providing reliable and a more precise cognitive performance analytic metrics to detect cognitive impairment.

BACKGROUND OF THE INVENTION

Presently eye tracking has been utilized in neuropsychological testing to measure cognitive performance when a test taker uses his eyes to track a moving icon or dot which moves along a prescribed smooth pursuit path as described in U.S. patent application Ser. Nos. 13/694,873; 13/694,462; 13/694,461; 13/507,991 and 13/506,840 all incorporated herein by reference. The state of the art in cognitive performance testing has provided clinicians and researchers with a more stable and accurate assessment of cognitive ability than heretofore possible, utilizing either the headset mounted apparatus of U.S. patent application Ser. No. 13/506,840 or the desktop apparatus described in U.S. patent application Ser. No. 13/507,991. It is now possible to monitor cognitive performance through the use of a number of measuring metrics, the most successful of which has been measuring the lead time or lag time of the eye as the eye attempts to track the smooth pursuit moving object. The lag time or lead time measurements while measuring cognitive performance may be improved upon by utilizing other ways of analyzing the data to pinpoint not only cognitive performance but also regions of the brain responsible for the cognitive performance results.

According to U.S. Pat. No. 7,819,818 by Jamshid Ghajar, one can use baselining to detect cognitive performance of a patient tracking a smooth pursuit object, usually utilizing standard deviation techniques. However, baselining as a metric, while useful, is not the only metric that is useful in measuring cognitive performance. As will be discussed, other metrics may be employed to pinpoint regions of the brain responsible for various cognitive impairment or abilities. It is only because of the use of the devices described in U.S. patent application Ser. Nos. 13/506,840 and 13/507,991 that one has the ability to robustly measure cognitive performance by any metric.

While the above describes current smooth pursuit eye tracking techniques, given the sensitivity and reliability of the newer neuropsychological testing techniques the following discussion details the state of the art in a generic manner so as to be able to describe the new measuring metrics of the subject invention.

Current state of the art and the analysis of cognitive variability, whether it's eye tracking or mechanical motion, is to use a data set consisting the x, y and t locations of the user's or the patient's eyes, finger or other body part that is being used to test cognition. This data is collected by either a mechanical system, or an eye tracker for instance looking at the eye, or by some analysis of sensors on the body as the body is moving in response to a test. The underlying premise of the analysis that is currently done is that the user is attempting to replicate with his or her own body, the motion or movement of a moving object that is moving in a way that is known as smooth pursuit movement. The resulting data file captures how well that patient is following or tracking the smooth pursuit-moving object.

There are a number of different paradigms for capturing the smooth pursuit eye movement: eye tracking, mechanical movement and a hybrid movement approach that is a combination of eye tracking and mechanical movement.

Eye Tracking

The eye tracking smooth pursuit eye movement analysis paradigm suggest that the test taker should follow a smoothly moving dot as it tracks across a display or screen with their eyes while cameras measure how well the eyes are moving in response to tracking the dot. It is presumed that this function requires higher order cognitive function in multiple parts of the brain from the eye, the optical cortex, the prefrontal lobe and the portion of the brain responsible for moving eye muscles. As the eye moves, the eye tracker trained on the eyes of the test taker generates the x, y location of the dark pupil, or light pupil, as well as the x and y location of the corneal reflection. This process of calculating the gaze of the test taker, called gaze transformation, tracks where the test taker's eyes was actually looking that can be used to analyze how far off the test taker was from the target he or she was supposed to be looking at.

Mechanical Movement

The hybrid movement is a hybrid approach of eye tracking and mechanical movement. The hybrid movement is the process by which a test is administered on a screen where the test taker is looking at the test on the screen to smoothly track the moving target on the screen with his or her eyes while simultaneously moving their hand, or other body part, to mechanically track the target. An input source is used to capture the movement of at least one or more points on the body for instance via an input source, such as a mouse, tablet, stylus, keyboard or turn wheel, as one takes the test.

This method of generating data files also produces a number of different opportunities for data analysis. The most specific data analysis is the comparison of the location of the primary source of mechanical input and the location of the target projected on the screen, which assesses the difference between where the target was and where the user was. This method in the hybrid sense can also be coupled with an eye tracker to generate a secondary set of data, where the test taker was actually looking during the test. This secondary set of data may even be two sets of data when individual data is taken per eye, one for the left eye and another for the right eye.

Independent of how smooth pursuit eye movement data was captured, the resulting data file typically contains x, y locations and time stamps of the test target as well as that of the test-taker. Currently the smooth pursuit eye movement data is analyzed for their continuity of motion, how well the test-taker follows the predicted path of the target controlled by the test administrator or test designer. The target path is of a smooth linear motion, which is sometimes curved and often times a motion that has a fixed speed over time.

Today the dominant method of analyzing the opto-cognitive test data files with respect to assessing cognitive performance or cognitive impairment is a metric known as smooth pursuit variability analysis. Variability analysis is the process of taking the differences in x, y, and radial distances between the target location and the patient's attempt to replicate that target location, which is measured by the tangents of the point distances between the target and the patient's attempt to replicate, then applying the standard deviation function that assesses what the degree of variability, or variance squared, are across the distances over the duration of the test. Thus, the degree of variability assesses whether the movements are at a predictable interval ahead or behind the target, or the movements are moving at variable distances sometimes behind and sometimes ahead of the target. A high degree of variability is reflected in a high standard deviation score.

This variability analysis calculation however is not a trivial one. Often times the input data source has noise or errors in the data that complicate the analysis. For example, for eye tracking data sets, the users blinking or saccading as covered in the prior art can introduce sources of noise, which must be detected and filtered out. For the mechanical movement and hybrid movement data sets, motion or mechanical sources of noises like spasms also need to be taken into consideration. Mechanical sources of noise may derive from various physical variables of the test-taker such as the test-taker's metabolic rate and the state of the muscle that would impact the smoothness of the data. Mechanical sources of noise too must be detected and filtered out in the data file. Once the data file has been filtered, the data must be smoothed in some way before it is ready for analysis. Smoothing the data in other words is to find and concatenate long runs of continuous data that are uninterrupted into a single sequence of data that can then be used for the purposes of analysis.

However, there is a problem with variability analysis. In variability calculation, the variability is compressed by the use of standard deviation formulas, which brings the test file down to a single or couple of numbers to characterize the test performance of the patient. Despite the objective of the application of standard deviation in the variability analysis of capturing the degree to which the patient is matching the location of the target in the smooth pursuit test, standard deviation unfortunately does not perform as desired, especially in cases where the patient is not doing well. This is because the standard deviation is a convex function. This means that the standard deviation function does not have an upper bound limit. Thus, the standard deviation function does not have an upper bound for how badly the patient performed on the test, but if the patient performs the test perfectly, the standard deviation will reflect a score of zero or an extremely low value. As a result, for every test and every patient, a baseline must be taken and the machine must be calibrated with respect to the frame rate per second, the time lag in between consecutive dots, and the magnitude of the difference in the dot in terms of pixels or degrees in order to first filter out those instances or at least to calibrate those instances where the standard deviation might be a large score. This is done to establish a relative upper bound of the standard deviation unique to the device and the patient. In fact, this creates a secondary metric, for instance a one to ten linear scale that can translate a standard deviation raw output score into a limited linearized scoring system based on the patient's performance.

Other simpler metrics other than variability analysis, or standard deviation, are sometimes employed in the analysis of these data files. For instance, mean, median, mode and other statistical measures are used to determine outliers usually assess the quality of the captured data file, run length sequence, and consecutive run length sequence. These measurements are generally used to assess the performance quality of the test-taker, quality of the data file, and the performance of the test to capture the patient's attempt to replicate the test without calculating cognitive performance. Such measurements have been described in the prior art.

SUMMARY OF INVENTION

This invention is a set of metrics designed to capture the features and behavior of the target versus the patient's movement in order to assess specific cognitive functions during the course of the test. In other words, the invention isolates the performance of the patient during the test taking process using different metrics instead of the current practice in opto-cognitive data analysis that compresses the performance of the patient into a single performance vector that might mask how the patient is varying in his or her performance in one way or another. Thus, the invention allows for a finer degree of granularity of understanding the patient's performance during an opto-cognitive smooth pursuit test. The set of component metrics or vectors described in the invention include lead trail statistic, radial inbounding, path dependent velocity, path drift, velocity variability, and variance statistics.

Lead Trail Statistic

Lead trail statistic is the analysis of how much the user was ahead or behind the target where at the moment the target was supposed to be. For instance, when the target is at a position around a smooth pursuit circle of 5 degrees during a circular smooth pursuit test and the test-taker is at 7 degrees, then that is a lead of 2 degrees. Instead, if the test-taker was at 3 degrees, then that is a trail of 2 degrees. These are examples of what is called a lead trail absolute amount. Using these lead trail absolute amounts, the data set of the test can be analyzed to show what percentage of lead and percentage of trail the user exhibited during the opto-cognitive testing. Thus, giving a specific assessment of whether the user was constantly leading or trailing throughout the test.

In addition, the lead trail absolute amount data can assess how often the test-taker changed from leading to trailing during the test, which metric is called lead trail flip-flop. In other words, lead trail flip-flop is how many times the user crossed the axis plane of leading into trailing the target, or vice versa. As the lead trail flip-flop is a representation of how sporadic or how predictable the user was in taking the smooth pursuit test, it allows for the analysis of characteristics that might be associated with cognitive disorders such as multiple sclerosis, epilepsy or Parkinson's disease.

Radial Inbounding

Radial inbounding is an assessment of how frequently the user was within a certain radius or distance from a smooth path, measured in terms of pixels, around where the target was throughout the test. For instance, if the radial threshold were set at ten pixels, then if the test-taker or user were eight pixels from the target, the success would be represented with the number one, but if the user were eleven pixels away from the target, the failure would be represented with a zero. This then allows one to observe how frequently the user was on target versus how frequently the user was drifting. This can also be used as a way to filter the signal, as it can be an assessment of the degree to which the user matches the target, then fails to match the target, and then re-matching the target, which is a pattern associated with fatigue.

Path Dependent Velocity

Path dependent velocity measures the speed with which the user tracks the velocity of the target as it progresses along a smooth path. In one embodiment the movement spans only a narrow corridor or range of target motion. It is an analytic metric specific to the ability of the patient to move at the speed of the target within a narrow range or bounded tunnel to the left and right, or sides of the target path. Thus, the comparison of the subject path dependent velocity gauges how well the patient is able to match the velocity of the target.

Path Drift

Path drift is a measurement of the drift or how far away from a normal to the curve of the target path the patient was. In other words, if the target path is assumed to have an instantaneous idealized normal vector, path drift is how far off to the left or the right the patient along a normal to the path. Thus the path drift measures the number of pixels off the patient is relative to the normal line to the path.

Velocity Variability

Velocity variability can be defined as velocity in a movement direction tangent to or parallel to the target path of the user measured by the velocity of a point on the target path which is a projection of the user point onto the target path. When the movement of the patient is in the direction of the vector or the line of the target path, this movement is considered parallel to the direction of the path and therefore that is the path velocity. The variability of this velocity in the direction only parallel to the path is called velocity variability. Note, velocity that is normal to the path is another valuable velocity component and corresponds to path drift 90 degrees to the right or the left. This then measures for instance, the drift variability or the deviation of the patient from the target path direction. Note further that any velocity variability may be indicative of lack of cognitive or conscious control of smooth pursuit movement towards a smoothly moving target.

Variance Statistics

Variance statistics typically analyze the change in or the rate of change in the movement or predictability of the patient movement in a specific direction. Thus, variance statistics includes generic statistical measures such as the mean, median, mode, standard deviation, variance and range of the patient performance. This gives some indication of the normalcy, repeatability or steadiness of the patient movement.

The six metrics described in the present invention are examples of how analysis utilizing these metrics can describe the behavior or the characteristics of the behavior of the patient as he or she is attempting to replicate a smooth pursuit movement.

The principle advantage of the use of the subject metrics involved in measuring a patient's attempt to replicate a target position is that the metric or vector can now be associated with different types of cognitive impairments more precisely. For example, cognitive impairment associated with path drift has been shown to be associated specifically to mild traumatic brain injury patients, while lead trail variability has been associated with fatigue. In addition, radial inbounding has been associated with fatigue or temporary attention deficit, and thus related to diagnosis of attention-related disorders such as ADD (Attention Deficit Disorder) and ADHD (Attention Deficit Hyperactivity Disorder). As shown, these metrics can be correlated to and analyzed to specific cognitive impairments, unlike current cognitive test analysis that simply relies on a single overarching standard deviation calculation as a brute force high level summary of the patient's performance.

Furthermore, as the invention is a set of metrics, this invention does not require the introduction of any new technology on the hardware or in data collection methods. The invention is instead an improvement on the analysis of the data files coming from any opto-cognitive testing device that generates x, y and t files such as an eye tracker, a mechanical tracker or a hybrid tracker. As a result, this invention can be used on existing data file techniques to allow for a more precise assessment of a specific cognitive impairment, rather than a generalized impairment state. This also allows for a more fine tuned baseline assessment or variability assessment in order to determine how specifically the patient is deviating from their baseline in a subsequent set of tests.

The results of using these metrics can be further analyzed using statistical methods associated with distribution or population demographic distributions introducing skew and ketosis as an assessment of where the patient's performance lies on a curve of population performances as expected given the patient's demographics. Such population demographics include age, sex, race or cognitive disposition.

The way of assessing cognitive performance of a patient is now thought in a new light. Rather than assessing the patient's performance in a single variable measure, the patient's performance is now assessed along a dimension of variables. This then allows greater granularity in one's ability to associate specific metrics with cognitive impairments because no cognitive impairment is the same and cognitive impairment can manifest itself in multiple ways in terms of performance impairments. This multivariate analysis thus allows for more fine tuned control over which specific performance metrics one measures the patient's cognitive state.

In summary, a method is provided for improving cognitive performance assessment in a smooth pursuit cognitive performance test by using measurement metrics including a lead/lag metric, a radial inbounding metric, a path dependent velocity metric, a path drift metric, a velocity variability metric, or a variance statistics metric.

BRIEF DESCRIPTION OF DRAWINGS

These and other features of the subject invention will be better understood in connection with the detailed description in conjunction with the drawings all of which:

FIG. 1 is a diagrammatic illustration of the types of cognitive performance measuring equipment and methodologies yielding x, y and t data which can be assessed utilizing the subject metrics for providing a cognitive performance signature based on the new metric;

FIG. 2 is a diagrammatic illustration of the new metrics utilizable in the analysis of cognitive performance, with the new metrics including lead/lag, radial inbounding, path dependent velocity, path drift, velocity variability and variance statistics, all relative to smooth pursuit path analysis.

FIG. 3 is a graph indicating lead/trail statistical analysis for use as a metric in measuring cognitive performance;

FIG. 4 is a graph of the radial inbounding metric for measuring cognitive performance;

FIG. 5 is a graph showing path dependent velocity as a metric for measuring cognitive performance;

FIG. 6 is a graph illustrating path drift as a metric for measuring cognitive performance;

FIG. 7 is a graph illustrating velocity variability as a metric for the measuring cognitive performance; and

FIG. 8 is a graph or scatter plot illustrating the utilization of variance statistics as a metric for measuring cognitive performance.

DETAILED DESCRIPTION OF DRAWINGS

Referring now to FIG. 1, the different types of data gathered through the utilization of various cognitive performance sensors is illustrated in which the data involves the use of a smooth pursuit path driven icon in which an individual 10 must trace the path of the moving icon, with the data involving x, y and t variables for the position of the icon on the path, as well as reflecting the ability of the individual to track the icon.

Here an individual 10 is the test taker whose cognitive performance is to be evaluated. As illustrated at 12 a hood containing a screen and eye tracking apparatus such as described in U.S. patent application Ser. No. 13/506,840 is utilized to assess the individual's ability to track the moving icon presented on the screen.

Likewise, as illustrated at 14 a desktop model involving an internally carried screen in which an icon follows a smooth pursuit path is viewed by individual 10, with eye tracking techniques utilized to assess the test taker's ability to track the moving icon. This device is described in U.S. patent application Ser. No. 13/507,991.

As illustrated at 22 a tablet may be utilized to present a path 26 on which a moving icon 28 travels, with the finger of the individual tracking the icon as it moves along the path. It will be appreciated that in this type of scenario the individual's ability to move his or her finger is dependent upon eye tracking as well as muscular coordination, all of which involving cognitive performance.

As shown at reference character 36 an fMRI having a sensing head 38 may be utilized to assess brain activity in individual 10 as for instance when the individual is presented with a moving icon on a screen, with the results of the fMRI being correlated to the ability of the individual's eyes to track the on-screen icon presented while taking the test.

On the other hand, an EEG setup may be utilized to measure the brain waves of the individual 10 as he tracks a moving icon on a screen.

It will be appreciated that all of the above rely on data having an x, y and t coordinate system to describe not only the smooth pursuit motion but also the ability of the individual's eyes to track the moving icon on a screen.

However, as shown at 42 an individual 10 may be asked to balance on a ball 44 or other balance device, with the data from his ability to balance on the device being captured in any one of a number of ways by indicating his position in space. This data also can be correlated to x, y and t data which can correspond to the individual tracking a smooth pursuit icon on a screen.

Regardless of the way in which the x, y and t data is available, this data may be analyzed by a metric 50, the result of which is a cognitive performance signature 52 that as illustrated at 54 may be correlated with a particular disease so as to arrive at a diagnosis 56.

It is the subject of the present invention to describe metrics that are utilizable with continuous data in an x, y and t format to be able to describe cognitive impairment in terms of the particular metric.

Referring now to FIG. 2, particular metrics involved in the data analysis method 60 are respectively a lead/lag metric 62, a radial inbounding metric 64, a path dependent velocity metric 66, a path drift metric 68, a velocity variability metric 70 and a variance statistics metric 72.

What is now presented is a description of the various metrics that are utilizable for data that has an x, y, and t format, which relates to smooth pursuit tracking of an icon along a path.

Referring now to FIG. 3, the lead trail statistic or the lead/lag statistic refers to how much the direction of gaze of an individual either leads or lags the smooth pursuit icon.

Lead Trail Statistic

U(x _(u) ,y _(u) ,t _(i))=User point

T(x _(t) ,y _(t) ,t _(i))=Target point

θ_(t)=angular displacement of T(x _(u) ,y _(u) ,t _(i))

θ_(u)=angular displacement of U(x _(t) ,y _(t) ,t _(i))

$\theta_{t} = {\tan^{- 1}\left( \frac{y_{t}}{x_{t}} \right)}$ $\theta_{u} = {\theta_{t} + {\tan^{- 1}\left( \frac{y_{u} - {R\; \sin \; \theta_{t}}}{x_{u} - {R\; \cos \; \theta_{t}}} \right)}}$ θ_(diff)=θ_(u)−θ_(t)

if θ_(diff)>0: lead

if θ_(diff)<0: lag

As can be seen from FIG. 3 the target path is illustrated at 100, whereas the user-tracking path is illustrated at 102. Here the point U is the user point at time t₁ and is labeled 104.

T on this diagram is the location of the target at t=1, namely t₁, here labeled 106. It will be noted that in the measurement of the lead/trail metric θ_(t) is the angle of displacement of the target point 106 measured along dotted line 108.

In order to establish the lead and lag time, the angle θ_(u) is the angular displacement of the user point at time t₁, here illustrated by dotted line 110.

It will be noted that if the difference between θ_(u) and θ_(t) is positive, then the user is leading the target and if the difference between θ_(u) and θ_(t) is negative then the user is lagging.

It is noted that lines 108 and 110 originate at a point 120, which in one embodiment is the icon viewing point. Note that point 120 is along the x-axis. Alternatively, point 120 can be defined to be the center of curvature of the target path. The center of the smooth pursuit path is determined by the smooth pursuit path algorithm. By the use of this algorithm one can calculate the shape of the path in terms of circles or sinusoids.

It is noted that the angle θ_(u) establishes is the point 104 at which the user was looking when he was tracking the target at time t₁. Thus the displacement of the user point relative to the target point is the lead or trail displacement of where the test taker is trying to view the moving icon as opposed to where the icon actually is. It will be appreciated that point 120 as it relates to the user point is located on the x, y coordinate of the graph on which data is presented, allowing capturing the movement of the eye in terms of the tracking device or stylus utilized.

Taking a look at the above equation, in U(x_(u), y_(u), t_(i)) U represents the user point as determined by eye tracking, whereas T(x_(t), y_(t), t₁) represents the location of the target point.

Then in this equation θ_(t) is angular displacement of the target point with respect to the x-axis, where the origin is at the center of rotation of the smooth pursuit path.

It will be appreciated that θ_(t) is equal to the arc tangent of y_(t)/x_(t) so that the angle is calculated based on the position of x and y of the target point. In short, θ_(t) is the angular displacement of the target point T(x_(u), y_(u), t₁) from the x-axis, whereas θ_(u) is the angular displacement of the user point U at x_(t), y_(t), t₁. The expression of θ_(u)=θ_(t)+arc tangent of y_(u)−R sin θ_(t)/x_(u)−R cos θ_(t) is a convenient way of defining θ_(u) in terms of θ_(t)+an arc tangent.

θ_(diff) is the difference between θ_(u)−θ_(t) such that if θ_(diff) is >0 one has a leading situation and if θ_(diff) is <0 one has a lagging situation.

θ_(diff) therefore is a metric, which is utilized to establish whether the test taking individual is leading or lagging the target. It is also a metric to indicate by how much the lead or lag is.

The next metric that is useful in cognitive performance evaluation is the so-called radial inbounding metric.

Radial Inbounding

r _(o)=√{square root over (x ² +y ²)}

if r _(o) ≦r _(t): within the radial bound

if r _(o) ≧r _(t): outside the radial bound

As can be seen in FIG. 4 radial inbounding includes a target path 100 and a user point path 102, with user point 104 being within the circular dotted line 122 centered on target point 106 that establishes the radial bound r_(t). Here the establishment of r_(t) creates a threshold relating to how far the user is allowed to be away from the target point 106 to constitute valid data. Note that user point 104 is the difference r₀ away from target point 106 and constitutes the radial distance between the target point and the user point.

The radial distance r₀ is calculated by taking the square root of x² plus y² so that in this case it will be taking the differences between the x values of the target and the user and the differences in the y values for the user and the target to find the distance between the user point 104 and a target point 106.

Note that if r₀ is less than r_(t) then the user point is within the radial bound, whereas if r₀ is greater than or equal to r_(t) then the user point is outside the radial bound.

The radial bound is important because it provides a threshold as to how far the user can be off of the target for a given condition. Alternatively, for instance it can show how the user is improving if the user point can stay within the radial inbounding distance provided by the radial inbounding circle 122.

In terms of a metric, as a simple metric, one can provide a binary indication of the user's ability to track the target by assigning a zero when the user is outside of the bound and a one when the user is inside the bound. The accumulation of data of zeros and ones therefore can indicate whether the user has been within or not within the threshold and therefore how well the user can track the moving icon.

The next metric that is important is path dependent velocity.

Path Dependent Velocity

U(x _(u) ,y _(u) ,t _(i))=User point

T(x _(t) ,y _(t) ,t _(i))=Target point

if U(x _(u) ,y _(u) ,t _(i)) is within path bound threshold,

${v_{i}({target})} = {\frac{x_{t_{i}} - x_{t_{i - 1}}}{t_{i} - t_{i - 1}}\mspace{14mu} {pixels}\text{/}{second}}$ ${v_{i}({user})} = {\frac{x_{u_{i}} - x_{u_{i - 1}}}{t_{i} - t_{i - 1}}\mspace{14mu} {pixels}\text{/}{second}}$

The purpose of the path dependent velocity metric is to establish how well the test taking individual moves his gaze to track the target by matching the velocity of the user's eyes or finger to the velocity of the target or vice versa. Here the target path is 100 and the user path is 102, with the instantaneous position of the target being shown at 106. Note that in order to establish the velocity at which the user is tracking the target one needs two user points on the user path. These user points are described here at point 130 and point 132 which is the position of the user point at time t₁ and time t₂, with the velocity of the user point at time t₂ being described by vector 136. Note that the velocity of the target is taken along a tangent to target line 100 at target point 106, with the velocity of target at point 106 being shown by vector 134. This velocity as indicated by vector 134 is compared to the velocity of vector 136 which is again tangent to curve 102 at point 132.

As can be seen from the equations U is a function of x_(u), y_(u), t_(i), where the target point T is a function of x_(t), y_(t) and t_(i).

Notice that there are path bound thresholds established by dash lines 140 and 142 These bounds act as a filter to filter out user point data that is aberrational or unlikely due to noise or other errors. Thus if a user point is within this bound threshold then one can use it to compare its velocity with the velocity of the target. Note this is shown in the equation as v_(i) (target) and v_(i) (user).

It will be appreciated that in one embodiment velocity is computed in terms of pixels per second, which gives a reasonable metric to compare the velocities. This is because if the user is too far from the target point then one can assume that it is either a calibration error or the user is simply way too far off and not tracking properly. In these two cases, comparison of the velocities does not relate to reliable data.

Note that the matching of the target velocity and the user point velocity is a way to measure how consistent or non-consistent the test taker is in being able to follow the target. The result is if the target is moving at a velocity x and the gaze point is moving at velocity x, then it can be concluded that the test taker is tracking reasonably well with the target in terms of velocity. Alternatively if the user's velocity varies from the target velocity, then this is a measure of how well the user is not tracking the target, noting of course if the user's velocity varies is outside certain threshold limits or bounds the data can be ignored.

As to path drift as a metric the following equations apply.

Path Drift

$\lambda_{u} = \frac{\left( {y_{u\; 2} - y_{u\; 1}} \right)}{\left( {x_{u\; 2} - x_{u\; 1}} \right)}$ b _(u) =y _(u2)−(λ_(u) x _(u2))

y _(u)=λ_(u) x+b _(u)

$y_{UPerp} = {{- \frac{x}{\lambda_{u}}} + b_{u}}$ r(θ)=target path equation

P(x _(t) ,y _(t))=intersection(y _(UPerp) ,r(θ))

Path Drift Magnitude=√{square root over ((y _(t) −y _(u2))²+(x _(t) −x _(u2))²)}{square root over ((y _(t) −y _(u2))²+(x _(t) −x _(u2))²)}

Referring now to FIG. 6 this metric seeks to establish how far off the user point path is from the target path, noting that the user point travels along path 102, whereas the target travels along path 100. Here the target point 106 is defined as T(x_(t), y_(t) and t₁), whereas the user point at user point 134 is defined by U(x_(u), y_(u), t). Note that the path drift is measured along a line 130, namely y_(UPerp), which is orthogonal to the target path such that dropping a line through point 132 intersects the target path at right angles. The point of intersection is labeled by point 136 and the path drift measured along line 130 between point 132 and 136 as shown by double ended arrow 140.

One can assess path drift on a point-by-point basis or one can calculate an average drift from these measured points. This metric can thus establish cognitive performance based on how far the user point path drifts from the target path. It is important to note that one is not comparing the distance of the user and the target points at the same timestamps. One is rather measuring the distance between a user point and the target path that is based off the user point data and a line orthogonal to the target path that passes through the user point.

The point of this measurement that one is trying to establish how far away the user path is from the target path instead of trying to find the distance between the user point and the target point at some particular time stamp. This may offer very skewed results depending on whether the user was very far off or very far ahead or behind the target. Note that data is taken at user point 130 to be able to establish vector 142, the normal to which establishes the distance 140.

In short, the purpose of determining path drift is to be able to represent how close the user path as a whole is to the target path as a whole.

One simple way of defining the utility of path drift is to consider a simple circular smooth pursuit test where one draws the user path on top of the target path. Assuming that one is filling in the holes between the user and target path, one can determine how far off the user is between these gaps. Thus one does not consider where at any given time the user points are with respect to the target path but rather the general shape of the user points and how far off the user points path is from the target path.

Velocity Variability

Unlike path dependent velocity, which measures the velocity of the user point on the user's path as he or she tracks an icon moving along a target path, velocity variability measures the velocity of the user point projected onto the target path.

It will be noted that the point of gaze of an individual when tracking an icon varies considerably as the individual tries to track the target point. In fact a plot of the user points along the target path are extremely variable both in position with respect to the target path and as to the instantaneous velocity of these points.

The result of utilizing eye tracking is that this user path variability creates a significant amount of noise, with the noise from the eye tracking coming from the drift of the individual's eye in and out as well as radial drift. While one can measure path drift as illustrated in FIG. 6, or one can filter out outlying user points in terms of path dependent velocity as illustrated n FIG. 5, it has been found that by projecting user points onto the target path and measuring the velocity of the intersection of a line from the user point through the target path orthogonal to the target path one can obtain a relatively noise free metric for measuring cognitive performance.

Thus, by transposing and mapping the point that the eye gaze follows down onto the target path one is eliminating all of the orthogonal noise from the eye tracking task to obtain a cleaner signal. With the reduction in noise one can then apply filtering analytics, which are higher performing because they are dealing with a cleaner input signal. This particular metric is important when one moves from a simple circle for the target path to a more complex shape such as a cloverleaf, a helix or a cyclical shape.

From FIG. 7 it will be seen that a target follows target path 100, whereas the user path 102 has a number drift variations both above and below the target path. As stated above, it is the purpose of the velocity variability metric to project a point on user path 102 onto target path 100. Here user point 150 is projected onto target path 100 as illustrated at 150′, by a line orthogonal to the target path whereas user point 152 is projected onto target path 100 as illustrated at 152′ and user point 154 is projected onto target path 100 as illustrated at 154′. In the projection, one drops a line through the user point that orthogonally intersects the target path.

The velocity of the projected points 150′, 152′ and 154′ have an associated velocity indicated respectively by vectors 160, 162 and 164. It is the velocity of the intersection of the projection of the user points onto the target path that is used to measure velocity. One is therefore be able to measure velocity variability, with the following equation measuring the instantaneous velocity at a particular intersection point followed by using a standard deviation technique to arrive at velocity.

$V_{o_{1}} = {{velocity} = \frac{d_{1} - d_{0}}{t_{1} - t_{0}}}$ ${velocity} = {{Std}.\mspace{14mu} {{dev}\left( {\sum\limits_{\cdot}^{v = k}v_{k}} \right)}}$

As to the variance statistics the following equations apply which are standard variance metrics.

Variance Statistics

${Mean} = {\frac{1}{n}{\sum\limits_{i = 1}^{n}x_{i}}}$ ${StandardDeviation} = \sqrt{\frac{1}{n}{\sum\limits_{i = 1}^{n}\left( {x_{i} - {{Mean}(x)}} \right)}}$ ${Variance} = {\frac{1}{n}{\sum\limits_{i = 1}^{n}\left( {x_{i} - {{Mean}(x)}} \right)}}$ Range=[Minimum(x),Maximum(x)]

First there is the mean, followed by the standard deviation, followed by the variance and followed by the range. These are standard statistical metrics that are used in the subject case to provide various metrics, which can have a particular correlation to a particular performance function. Note that as illustrated in FIG. 8 a scatter pot of the data gives a general backbone structure of what the data set is that one is looking at. Basically depending on its relationship to the circle 180 the data set describes how statistically significant the data is with respect to some metric.

As to the variance statistics the following equations apply which are standard variance metrics. First there is the mean, followed by the standard deviation, followed by the variance and followed by the range. These are standard statistical metrics that are used in the subject case to provide various metrics, which can have a particular correlation to a particular performance function. Note that as illustrated in FIG. 8 a scatter pot of the data gives a general backbone structure of what the data set is that one is looking at. Basically depending on its relationship to the circle 180 the data set describes how statistically significant the data is with respect to some metric. 

What is claimed is:
 1. In a system for measuring cognitive performance in terms of the ability of an individual to track an icon which moves along a target path, a system for determining cognitive performance by measuring the ability of said individual to track said icon, comprising: a specialized processor for determining as a measurement metric the lead or lag of the gaze point of the patient with respect to the position of the icon on said target path.
 2. In a system for measuring cognitive performance in terms of the ability of an individual to track an icon which moves along a target path, a system for determining cognitive performance by measuring the ability of said individual to track said icon, comprising: a specialized processor for determining as a measurement metric the radial distance of the gaze point of said individual with respect to said target path.
 3. In a system for measuring cognitive performance in terms of the ability of an individual to track an icon which moves along a target path, a system for determining cognitive performance by measuring the ability of said individual to track said icon, comprising: a specialized processor for determining as a measurement metric the path dependent velocity of the gaze point of said individual with respect to the velocity of the icon on said target path.
 4. In a system for measuring cognitive performance in terms of the ability of an individual to track an icon which moves along a target path, a system for determining cognitive performance by measuring the ability of said individual to track said icon, comprising: a specialized processor for determining as a measurement metric the path drift of the path of the gaze point of said individual with respect to said target path.
 5. In a system for measuring cognitive performance in terms of the ability of an individual to track an icon which moves along a target path, a system for determining cognitive performance by measuring the ability of said individual to track said icon, comprising: a specialized processor for determining as a measurement metric the velocity variability of a projection of the gaze point of said individual onto said target path.
 6. In a system for measuring cognitive performance in terms of the ability of an individual to track an icon which moves along a target path, a system for determining cognitive performance by measuring the ability of said individual to track said icon, comprising: a specialized processor for taking the results of the determination of cognitive performance using a metric of one of lead lag performance, radial inbounding performance, path dependent velocity performance, path drift performance and velocity variability performance, and applying variance statistics comprising one of mean, standard deviation, variance and range to the results of using said metric.
 7. A method comprising cognitive performance assessment in a smooth pursuit cognitive performance test by using a measurement metric including one of a lead/lag metric, a radial inbounding metric, a path dependent velocity metric, a path drift metric, a velocity variability metric or a variance statistics metric. 